Demands for an adhesive which is cured at room temperature in a short period of time are increasing from the viewpoint of an improvement in the production line efficiency and the cost reduction. Heretofore, well know as a room temperature quick curing adhesive are a two-part type quick curing epoxy adhesive, an instantaneous adhesive, an anaerobic adhesive, a non-anaerobic acrylic adhesive, etc.
A two-part type quick curing epoxy adhesive is used by weighing and mixing a main agent and a curing agent, and if weighing or mixing is not sufficiently carried out, the strength may remarkably be decreased. Further, even if weighing and mixing are sufficiently carried out, the peel strength and the impact strength tend to be low.
An instantaneous adhesive has excellent workability but has low peel strength and impact strength in general and is poor in the heat resistance and the moisture resistance, and accordingly the range of its use is remarkably limited.
An anaerobic adhesive is an adhesive which is cured by being pressure-bonded by materials to be bonded to shut off the air, and of course, a portion which is in contact with the air such as a running-over portion is not cured. Accordingly, in the case of a porous adherend or a high balance between adherends, it will not sufficiently be cured, thus leading to failure in adhesion.
A non-anaerobic acrylic adhesive is generally called a second-generation acrylic adhesive (SGA). Although it is two-part type, it has excellent workability such that no accurate weighing of two agents is required, and the adhesive is cured at room temperature in several minutes to several tens minutes by very rough weighing and mixing. In addition, it has high peel strength and impact strength, and a running-over portion is well cured. Thus, it has been widely used.
However, regarding an acrylic adhesive having a curing time of from several minutes to several tens minutes at room temperature, demands on one having a further shortened curing time are increasing from the viewpoint of an improvement in the production line efficiency and the cost reduction.
For example, an adhesive as disclosed in Patent Document 1 comprises an urethane acrylate, an acrylic ester monomer, an aromatic perester, an organic acid and a transition metal, and is cured in a set time of 45 seconds.
Further, an adhesive as disclosed in Patent Document 2 comprises a specific urethane acrylate, an acrylic ester monomer, a peroxyester and an accelerator made of a compound forming a redox system, and is also cured in a short set time within 1 minute.
An adhesive composition as disclosed in Patent Document 3 comprises a mixture of a chlorosulfonated polyethylene and a specific acrylic monomer in a specific proportion, cumene hydroperoxide, an aldehyde-amine condensate and an oxidizing organic compound of a transition metal, and is disclosed to be cured in a curing time of several seconds.
Patent Documents 4 and 5 disclose that a quick curing acrylic adhesive can be obtained by mixing a peroxyester, a reaction condensate of an amine and an aldehyde, a salt of copper and an aromatic hydroxy group-containing compound with an acrylic monomer.
Patent Document 1: U.S. Pat. No. 4,348,503
Patent Document 2: JP-A-60-199085
Patent Document 3: JP-A-55-065277
Patent Document 4: JP-A-03-134080
Patent Document 5: JP-A-03-134081